Two Dimensional Shift Array for Image Processor

ABSTRACT

An apparatus is described. The apparatus includes an execution lane array coupled to a two dimensional shift register array structure. Locations in the execution lane array are coupled to same locations in the two-dimensional shift register array structure such that different execution lanes have different dedicated registers.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority to U.S. patentapplication Ser. No. 14/694,750, filed on Apr. 23, 2015, the entirecontents of which are hereby incorporated by reference.

FIELD OF INVENTION

The field of invention pertains generally to image processing, and, morespecifically, to a two dimensional shift array for an image processor.

BACKGROUND

Image processing typically involves the processing of pixel values thatare organized into an array. Here, a spatially organized two dimensionalarray captures the two dimensional nature of images (additionaldimensions may include time (e.g., a sequence of two dimensional images)and data type (e.g., colors). In a typical scenario, the arrayed pixelvalues are provided by a camera that has generated a still image or asequence of frames to capture images of motion. Traditional imageprocessors typically fall on either side of two extremes.

A first extreme performs image processing tasks as software programsexecuting on a general purpose processor or general purpose-likeprocessor (e.g., a general purpose processor with vector instructionenhancements). Although the first extreme typically provides a highlyversatile application software development platform, its use of finergrained data structures combined with the associated overhead (e.g.,instruction fetch and decode, handling of on-chip and off-chip data,speculative execution) ultimately results in larger amounts of energybeing consumed per unit of data during execution of the program code.

A second, opposite extreme applies fixed function hardwired circuitry tomuch larger blocks of data. The use of larger (as opposed to finergrained) blocks of data applied directly to custom designed circuitsgreatly reduces power consumption per unit of data. However, the use ofcustom designed fixed function circuitry generally results in a limitedset of tasks that the processor is able to perform. As such, the widelyversatile programming environment (that is associated with the firstextreme) is lacking in the second extreme.

A technology platform that provides for both highly versatileapplication software development opportunities combined with improvedpower efficiency per unit of data remains a desirable yet missingsolution.

SUMMARY

An apparatus is described, The apparatus includes means for shifting, ina same direction and number of locations, data from multiple contiguouslocations within a two-dimensional shift register array structure toprovide each of multiple different execution lanes within an executionlane array a new value within respective dedicated registers of themultiple different execution lanes. The different execution lanes arecoupled to their respective dedicated registers at same respectivelocations of the execution lane array and the two-dimensional shiftregister array.

An apparatus is described, The apparatus includes an execution lanearray coupled to a two dimensional shift register array structure.Locations in the execution lane array are coupled to same locations inthe two-dimensional shift register array structure such that differentexecution lanes have different dedicated registers.

LIST OF FIGURES

The following description and accompanying drawings are used toillustrate embodiments of the invention. In the drawings:

FIG. 1 shows an embodiment of an image processor hardware architecture;

FIGS. 2 a, 2 b, 2 c, 2 d and 2 e depict the parsing of image data into aline group, the parsing of a line group into a sheet and the operationperformed on a sheet with overlapping stencils;

FIG. 3 shows an embodiment of a stencil processor;

FIG. 4 shows an embodiment of a data computation unit within a stencilprocessor;

FIGS. 5 a, 5 b, 5 c, 5 d, 5 e, 5 f, 5 g, 5 h, 5 i, 5 j and 5 k depict anexample of the use of a two-dimensional shift array and an executionlane array to determine a pair of neighboring output pixel values withoverlapping stencils;

FIG. 6 shows an embodiment of a unit cell for an integrated executionlane array and two-dimensional shift array;

FIG. 7a depicts a first two dimensional register array structureinterconnection scheme;

FIG. 7b depicts a second two dimensional register array structureinterconnection scheme;

FIG. 8a depicts a first row or column of a two-dimensional registerarray structure;

FIG. 8b depicts a second row or column of a two-dimensional registerarray structure;

FIG. 8c depicts the row of FIG. 8b coupled to a memory unit;

FIG. 8d shows another torpid embodiment;

FIG. 8e shows a power conservation circuit;

FIG. 9 shows an embodiment of a computing system.

DETAILED DESCRIPTION a. Image Processor Hardware Architecture andOperation

FIG. 1 shows an embodiment of an architecture 100 for an image processorimplemented in hardware. The image processor may be targeted, forexample, by a compiler that converts program code written for a virtualprocessor within a simulated environment into program code that isactually executed by the hardware processor. As observed in FIG. 1, thearchitecture 100 includes a plurality of line buffer units 101_1 through101_M interconnected to a plurality of stencil processor units 102_1through 102_N and corresponding sheet generator units 103_1 through103_N through a network 104 (e.g., a network on chip (NOC) including anon chip switch network, an on chip ring network or other kind ofnetwork). In an embodiment, any line buffer unit may connect to anysheet generator and corresponding stencil processor through the network104.

In an embodiment, program code is compiled and loaded onto acorresponding stencil processor 102 to perform the image processingoperations earlier defined by a software developer (program code mayalso be loaded onto the stencil processor's associated sheet generator103, e.g., depending on design and implementation). In at least someinstances an image processing pipeline may be realized by loading afirst kernel program for a first pipeline stage into a first stencilprocessor 102_1, loading a second kernel program for a second pipelinestage into a second stencil processor 102_2, etc. where the first kernelperforms the functions of the first stage of the pipeline, the secondkernel performs the functions of the second stage of the pipeline, etc,and additional control flow methods are installed to pass output imagedata from one stage of the pipeline to the next stage of the pipeline.

In other configurations, the image processor may be realized as aparallel machine having two or more stencil processors 102_1, 102_2operating the same kernel program code, For example, a highly dense andhigh data rate stream of image data may be processed by spreading framesacross multiple stencil processors each of which perform the samefunction.

In yet other configurations, essentially any DAG of kernels may beloaded onto the hardware processor by configuring respective stencilprocessors with their own respective kernel of program code andconfiguring appropriate control flow hooks into the hardware to directoutput images from one kernel to the input of a next kernel in the DAGdesign.

As a general flow, frames of image data are received by a macro I/O unit105 and passed to one or more of the line buffer units 101 on a frame byframe basis. A particular line buffer unit parses its frame of imagedata into a smaller region of image data, referred to as a “a linegroup”, and then passes the line group through the network 104 to aparticular sheet generator. A complete or “full” singular line group maybe composed, for example, with the data of multiple contiguous completerows or columns of a frame (for simplicity the present specificationwill mainly refer to contiguous rows). The sheet generator furtherparses the line group of image data into a smaller region of image data,referred to as a “sheet”, and presents the sheet to its correspondingstencil processor.

In the case of an image processing pipeline or a DAG flow having asingle input, generally, input frames are directed to the same linebuffer unit 101_1 which parses the image data into line groups anddirects the line groups to the sheet generator 103_1 whose correspondingstencil processor 102_1 is executing the code of the first kernel in thepipeline/DAG. Upon completion of operations by the stencil processor102_1 on the line groups it processes, the sheet generator 103_1 sendsoutput line groups to a “downstream” line buffer unit 101_2 (in some usecases the output line group may be sent back to the same line bufferunit 101_1 that earlier had sent the input line groups).

One or more “consumer” kernels that represent the next stage/operationin the pipeline/DAG executing on their own respective other sheetgenerator and stencil processor (e.g., sheet generator 103_2 and stencilprocessor 102_2) then receive from the downstream line buffer unit 101_2the image data generated by the first stencil processor 102_1. In thismanner, a “producer” kernel operating on a first stencil processor hasits output data forwarded to a “consumer” kernel operating on a secondstencil processor where the consumer kernel performs the next set oftasks after the producer kernel consistent with the design of theoverall pipeline or DAG.

A stencil processor 102 is designed to simultaneously operate onmultiple overlapping stencils of image data. The multiple overlappingstencils and, internal hardware processing capacity of the stencilprocessor effectively determines the size of a sheet. Here, within astencil processor 102, arrays of execution lanes operate in unison tosimultaneously process the image data surface area covered by themultiple overlapping stencils.

As will be described in more detail below, in various embodiments,sheets of image data are loaded into a two-dimensional register arraystructure within the stencil processor 102. The use of sheets and thetwo-dimensional register array structure is believed to effectivelyprovide for power consumption improvements by moving a large amount ofdata into a large amount of register space as, e.g., a single loadoperation with processing tasks performed directly on the dataimmediately thereafter by an execution lane array. Additionally, the useof an execution lane array and corresponding register array provide fordifferent stencil sizes that are easily programmable/configurable.

FIGS. 2a through 2e illustrate at a high level embodiments of both theparsing activity of a line buffer unit 101, the finer grained parsingactivity of a sheet generator unit 103 as well as the stencil processingactivity of the stencil processor 102 that is coupled to the sheetgenerator unit 103.

FIG. 2a depicts an embodiment of an input frame of image data 201. FIG.2a also depicts an outline of three overlapping stencils 202 (eachhaving a dimension of 3 pixels×3 pixels) that a stencil processor isdesigned to operate over. The output pixel that each stencilrespectively generates output image data for is highlighted in solidblack. For simplicity, the three overlapping stencils 202 are depictedas overlapping only in the vertical direction. It is pertinent torecognize that in actuality a stencil processor may be designed to haveoverlapping stencils in both the vertical and horizontal directions.

Because of the vertical overlapping stencils 202 within the stencilprocessor, as observed in FIG. 2 a, there exists a wide band of imagedata within the frame that a single stencil processor can operate over.As will be discussed in more detail below, in an embodiment, the stencilprocessors process data within their overlapping stencils in a left toright fashion across the image data (and then repeat for the next set oflines, in top to bottom order). Thus, as the stencil processors continueforward with their operation, the number of solid black output pixelblocks will grow right-wise horizontally. As discussed above, a linebuffer unit 101 is responsible for parsing a line group of input imagedata from an incoming frame that is sufficient for the stencilprocessors to operate over for an extended number of upcoming cycles. Anexemplary depiction of a line group is illustrated as a shaded region203. In an embodiment, the line buffer unit 101 can comprehend differentdynamics for sending/receiving a line group to/from a sheet generator.For example, according to one mode, referred to as “full group”, thecomplete full width lines of image data are passed between a line bufferunit and a sheet generator. According to a second mode, referred to as“virtually tall”, a line group is passed initially with a subset of fullwidth rows. The remaining rows are then passed sequentially in smaller(less than full width) pieces.

With the line group 203 of the input image data having been defined bythe line buffer unit and passed to the sheet generator unit, the sheetgenerator unit further parses the line group into finer sheets that aremore precisely fitted to the hardware limitations of the stencilprocessor. More specifically, as will be described in more detailfurther below, in an embodiment, each stencil processor consists of atwo dimensional shift register array. The two dimensional shift registerarray essentially shifts image data “beneath” an array of executionlanes where the pattern of the shifting causes each execution lane tooperate on data within its own respective stencil (that is, eachexecution lane processes on its own stencil of information to generatean output for that stencil). In an embodiment, sheets are surface areasof input image data that “fill” or are otherwise loaded into the twodimensional shift register array.

As will be described in more detail below, in various embodiments, thereare actually multiple layers of two dimensional register data that canbe shifted on any cycle, For convenience, much of the presentdescription will simply use the term “two-dimensional shift register”and the like to refer to structures that have one or more such layers oftwo-dimensional register data that can be shifted.

Thus, as observed in FIG. 2 b, the sheet generator parses an initialsheet 204 from the line group 203 and provides it to the stencilprocessor (here, the sheet of data corresponds to the shaded region thatis generally identified by reference number 204). As observed in FIGS.2c and 2 d, the stencil processor operates on the sheet of input imagedata by effectively moving the overlapping stencils 202 in a left toright fashion over the sheet. As of FIG. 2 d, the number of pixels forwhich an output value could be calculated from the data within the sheetis exhausted (no other pixel positions can have an output valuedetermined from the information within the sheet). For simplicity theborder regions of the image have been ignored.

As observed in FIG. 2e the sheet generator then provides a next sheet205 for the stencil processor to continue operations on. Note that theinitial positions of the stencils as they begin operation on the nextsheet is the next progression to the right from the point of exhaustionon the first sheet (as depicted previously in FIG. 2d ). With the newsheet 205, the stencils will simply continue moving to the right as thestencil processor operates on the new sheet in the same manner as withthe processing of the first sheet.

Note that there is some overlap between the data of the first sheet 204and the data of the second sheet 205 owing to the border regions ofstencils that surround an output pixel location. The overlap could behandled simply by the sheet generator re-transmitting the overlappingdata twice. In alternate implementations, to feed a next sheet to thestencil processor, the sheet generator may proceed to only send new datato the stencil processor and the stencil processor reuses theoverlapping data from the previous sheet.

b. Stencil Processor Design and Operation

FIG. 3 shows an embodiment of a stencil processor architecture 300. Asobserved in FIG. 3, the stencil processor includes a data computationunit 301, a scalar processor 302 and associated memory 303 and an I/Ounit 304. The data computation unit 301 includes an array of executionlanes 305, a two-dimensional shift array structure 306 and separaterandom access memories 307 associated with specific rows or columns ofthe array.

The I/O unit 304 is responsible for loading “input” sheets of datareceived from the sheet generator into the data computation unit 301 andstoring “output” sheets of data from the stencil processor into thesheet generator. In an embodiment the loading of sheet data into thedata computation unit 301 entails parsing a received sheet intorows/columns of image data and loading the rows/columns of image datainto the two dimensional shift register structure 306 or respectiverandom access memories 307 of the rows/columns of the execution lanearray (described in more detail below). If the sheet is initially loadedinto memories 307, the individual execution lanes within the executionlane array 305 may then load sheet data into the two-dimensional shiftregister structure 306 from the random access memories 307 whenappropriate (e.g., as a load instruction just prior to operation on thesheet's data). Upon completion of the loading of a sheet of data intothe register structure 306 (whether directly from a sheet generator orfrom memories 307), the execution lanes of the execution lane array 305operate on the data and eventually “write back” finished data as a sheetdirectly back to the sheet generator, or, into the random accessmemories 307. If the later the I/O unit 304 fetches the data from therandom access memories 307 to form an output sheet which is thenforwarded to the sheet generator.

The scalar processor 302 includes a program controller 309 that readsthe instructions of the stencil processor's program code from scalarmemory 303 and issues the instructions to the execution lanes in theexecution lane array 305. In an embodiment, a single same instruction isbroadcast to all execution lanes within the array 305 to effect aSIMD-like behavior from the data computation unit 301. In an embodiment,the instruction format of the instructions read from scalar memory 303and issued to the execution lanes of the execution lane array 305includes a very-long-instruction-word (VLIW) type format that includesmore than one opcode per instruction. In a further embodiment, the VLIWformat includes both an ALU opcode that directs a mathematical functionperformed by each execution lane's ALU (which, as described below, in anembodiment may specify more than one traditional ALU operation) and amemory opcode (that directs a memory operation for a specific executionlane or set of execution lanes).

The term “execution lane” refers to a set of one or more execution unitscapable of executing an instruction (e.g., logic circuitry that canexecute an instruction) An execution lane can, in various embodiments,include more processor-like functionality beyond just execution units,however. For example, besides one or more execution units, an executionlane may also include logic circuitry that decodes a receivedinstruction, or, in the case of more MIMD-like designs, logic circuitrythat fetches and decodes an instruction. With respect to MIMD-likeapproaches, although a centralized program control approach has largelybeen described herein, a more distributed approach may be implemented invarious alternative embodiments (e.g., including program code and aprogram controller within each execution lane of the array 305).

The combination of an execution lane array 305, program controller 309and two dimensional shift register structure 306 provides a widelyadaptable/configurable hardware platform for a broad range ofprogrammable functions. For example, application software developers areable to program kernels having a wide range of different functionalcapability as well as dimension (e.g., stencil size) given that theindividual execution lanes are able to perform a wide variety offunctions and are able to readily access input image data proximate toany output array location.

Apart from acting as a data store for image data being operated on bythe execution lane array 305, the random access memories 307 may alsokeep one or more look-up tables. In various embodiments one or morescalar look-up tables may also be instantiated within the scalar memory303.

A scalar look-up involves passing the same data value from the samelook-up table from the same index to each of the execution lanes withinthe execution lane array 305. In various embodiments, the VLIWinstruction format described above is expanded to also include a scalaropcode that directs a look-up operation performed by the scalarprocessor into a scalar look-up table. The index that is specified foruse with the opcode may be an immediate operand or fetched from someother data storage location. Regardless, in an embodiment, a look-upfrom a scalar look-up table within scalar memory essentially involvesbroadcasting the same data value to all execution lanes within theexecution lane array 305 during the same clock cycle. Additional detailsconcerning use and operation of look-up tables is provided furtherbelow.

FIG. 4 shows an embodiment of a data computation component 401. Asobserved in FIG. 4, the data computation component 401 includes an arrayof execution lanes 405 that are logically positioned “above” atwo-dimensional shift register array structure 406. As discussed above,in various embodiments, a sheet of image data provided by a sheetgenerator is loaded into the two-dimensional shift register 406. Theexecution lanes then operate on the sheet data from the registerstructure 406.

The execution lane array 405 and shift register structure 406 are fixedin position relative to one another. However, the data within the shiftregister array 406 shifts in a strategic and coordinated fashion tocause each execution lane in the execution lane array to process adifferent stencil within the data. As such, each execution lanedetermines the output image value for a different pixel in the outputsheet being generated. From the architecture of FIG. 4 it should beclear that overlapping stencils are not only arranged vertically butalso horizontally as the execution lane array 405 includes verticallyadjacent execution lanes as well as horizontally adjacent executionlanes.

Some notable architectural features of the data computation unit 401include the shift register structure 406 having wider dimensions thanthe execution lane array 405. That is, there is a “halo” of registers409 outside the execution lane array 405. Although the halo 409 is shownto exist on two sides of the execution lane array, depending onimplementation, the halo may exist on less (one) or more (three or four)sides of the execution lane array 405. The halo 405 serves to provide“spill-over” space for data that spills outside the bounds of theexecution lane array 405 as the data is shifting “beneath” the executionlanes 405. As a simple case, a 5×5 stencil centered on the right edge ofthe execution lane array 405 will need four halo register locationsfurther to the right when the stencil's leftmost pixels are processed.For ease of drawing, FIG. 4 shows the registers of the right side of thehalo as only having horizontal shift connections and registers of thebottom side of the halo as only having vertical shift connections when,in a nominal embodiment, registers on either side (right, bottom) wouldhave both horizontal and vertical connections.

Additional spill-over room is provided by random access memories 407that are coupled to each row and/or each column in the array, orportions thereof (e.g., a random access memory may be assigned to a“region” of the execution lane array that spans 4 execution lanes rowwise and 2 execution lanes column wise). For simplicity the remainder ofthe application will refer mainly to row and/or column based allocationschemes). Here, if an execution lane's kernel operations require it toprocess pixel values outside of the two-dimensional shift register array406 (which some image processing routines may require) the plane ofimage data is able to further spill-over, e.g., from the halo region 409into random access memory 407. For example, consider a 6×6 stencil wherethe hardware includes a halo region of only four storage elements to theright of an execution lane on the right edge of the execution lanearray. In this case, the data would need to be shifted further to theright off the right edge of the halo 409 to fully process the stencil.Data that is shifted outside the halo region 409 would then spill-overto random access memory 407. Other applications of the random accessmemories 407 and the stencil processor of FIG. 3 are provided furtherbelow.

FIGS. 5a through 5k demonstrate a working example of the manner in whichimage data is shifted within the two dimensional shift register array“beneath” the execution lane array as alluded to above. As observed inFIG. 5 a, the data contents of the two dimensional shift array aredepicted in a first array 507 and the execution lane array is depictedby a frame 505. Also, two neighboring execution lanes 510 within theexecution lane array are simplistically depicted. In this simplisticdepiction 510, each execution lane includes a register R1 that canaccept data from the shift register, accept data from an ALU output(e.g., to behave as an accumulator across cycles), or write output datainto an output destination.

Each execution lane also has available, in a local register R2, thecontents “beneath” it in the two dimensional shift array. Thus, R1 is aphysical register of the execution lane while R2 is a physical registerof the two dimensional shift register array. The execution lane includesan ALU that can operate on operands provided by R1 and/or R2. As will bedescribed in more detail further below, in an embodiment the shiftregister is actually implemented with multiple (a “depth” of)storage/register elements per array location but the shifting activityis limited to one plane of storage elements (e.g., only one plane ofstorage elements can shift per cycle). FIGS. 5a through 5k depict one ofthese deeper register locations as being used to store the resultant Xfrom the respective execution lanes. For illustrative ease the deeperresultant register is drawn alongside rather than beneath itscounterpart register R2.

FIGS. 5a through 5k focus on the calculation of two stencils whosecentral position is aligned with the pair of execution lane positions511 depicted within the execution lane array. For ease of illustration,the pair of execution lanes 510 are drawn as horizontal neighbors whenin fact, according to the following example, they are verticalneighbors.

As observed initially in FIG. 5 a, the execution lanes are centered ontheir central stencil locations.

FIG. 5b shows the following object code executed by both executionlanes:

  // thread X1: process stencil 1// shift down 1 shift right 1 load //put A in R1 // thread X2: process stencil 2// shift down 1 shift right1, load // put F in R1

As observed in FIG. 5b the program code of both execution lanes causesthe data within the shift register array to shift down one position andshift right one position. This aligns both execution lanes to the upperleft hand corner of their respective stencils. The program code thencauses the data that is located (in R2) in their respective locations tobe loaded into R1.

As observed in FIG. 5c the following program code next causes the pairof execution lanes to shift the data within the shift register array oneunit to the left Which causes the value to the right of each executionlane's respective position to be shifted into each execution lane'position:

  // thread X1: process stencil 1// shift down 1 shirt right 1 load //put A in R1 shift left 1 R1<= ADD R1, R2 // add A, B // thread X2:process stencil 2// shift down 1 shift right 1 load // put F in R1 shiftleft 1 R1<= ADD R1, R2 // add F, G

The value in R1 (previous value) is then added with the new value thathas shifted into the execution lane's position (in R2). The resultant iswritten into R1.

As observed in FIG. 5d the same process as described above for FIG. 5cis repeated using the following program code, which causes the resultantR1 to now include the value A+B+C in the upper execution lane and F+G+Hin the lower execution lane:

  // thread X1: process stencil 1// . . . R1<= ADD R1, R2 // add A, Bshift left 1 R1<= ADD R1, R2 // add C // thread X2: process stencil 2//. . . R1<= ADD R1, R2 // add F, G shift left 1 R1<= ADD R1, R2 // add H

At this point both execution lanes have processed the upper row of theirrespective stencils. Note the spill-over into a halo region on the leftside of the execution lane array (if one exists on the left hand side)or into random access memory if a halo region does not exist on the lefthand side of the execution lane array.

As observed in FIG. 5 e, the following program code next causes the datawithin the shift register array to shift one unit up which causes bothexecution lanes to be aligned with the right edge of the middle row oftheir respective stencils:

  // thread X1: process stencil 1// . . . R1<= ADD R1, R2 // add A, Bshift left 1 R1<= ADD R1, R2 // add C shift up 1 R1<= ADD R1, R2 // addH // thread X2: process stencil 2// . . . R1<= ADD R1, R2 // add F, Gshift left 1 R1<= ADD R1, R2 // add H shift up 1 R1<= ADD R1, R2 // addM

Register R1 of both execution lanes currently includes the summation ofthe stencil's top row and the middle row's rightmost value.

FIGS. 5f and 5g demonstrate continued progress moving leftwise acrossthe middle row of both execution lane's stencils. FIG. 5f showsexecution of the following program code:

  // thread X1: process stencil 1// . . . shift right 1 R1<= ADD R1, R2// ADD G // thread X2: process stencil 2// . . . shift right 1 R1<= ADDR1, R2 // ADD L

FIG. 5g shows execution of the following program code:

  // thread X1: process stencil 1// . . . shift right 1 R1<= ADD R1, R2// ADD F // thread X2: process stencil 2// . . . shift right 1 R1<= ADDR1, R2 // ADD K

The accumulative addition continues such that at the end of processingof FIG. 5g both execution lanes include the summation of the values ofthe top row and the middle row of their respective stencils.

FIG. 5h shows another shift to align each execution lane with itscorresponding stencil's lowest row using the following program code:

  // thread X1: process stencil 1// . . . shift up 1 R1<= ADD R1, R2 //ADD K // thread X2: process stencil 2// . . . shift up 1 R1<= ADD R1, R2// ADD P

FIGS. 5i and 5j show continued shifting to complete processing over thecourse of both execution lanes' stencils. FIG. 5i shows execution of thefollowing program code:

  // thread X1: process stencil 1// . . . shift left 1 R1<= ADD R1, R2// ADD L // thread X2: process stencil 2// . . . shift left 1 R1<= ADDR1, R2 // ADD Q

FIG. 5j shows execution of the following program code:

  thread X1: process stencil 1// . . . shift left 1 R1<= ADD R1, R2 //ADD M R1<= DIV R1, 9 // thread X2: process stencil 2// . . . shift left1 R1<= ADD R1, R2 // ADD R R1<= DIV R1, 9

FIG. 5k shows additional shifting using the following program code toalign each execution lane with its correct position in the data arrayand write the resultant thereto:

  // thread X1: process stencil 1// . . . shift right 1 shift down 1 X<=store R1 // thread X2: process stencil 2// . . . shift right 1 shiftdown 1 X<= store R1

In the example of FIGS. 5a-5k note that the object code for the shiftoperations may include an instruction format that identifies thedirection and magnitude of the shift expressed in (X, Y) coordinates.For example, the object code for a shift up by one location may beexpressed in object code as SHIFT 0, +1. As another example, a shift tothe right by one location may expressed in object code as SHIFT +1, 0.In various embodiments shifts of larger magnitude may also be specifiedin object code (e.g., SHIFT 0, +2). Here, if the 2D shift registerhardware only supports shifts by one location per cycle, the instructionmay be interpreted by the machine to require multiple cycle execution,or, the 2D shift register hardware may be designed to support shifts bymore than one location per cycle. Embodiments of the later are describedin more detail further below.

FIG. 6a shows another, more detailed depiction of the unit cell for thearray execution lane and shift register structure (registers in the haloregion do not include a corresponding execution lane). The executionlane and the register space associated with each location in theexecution lane array is, in an embodiment, implemented by instantiatingthe circuitry observed in FIG. 6a at each node of the execution lanearray. As observed in FIG. 6 a, the unit cell includes an execution lane601 coupled to a register file 602 consisting of four registers R2through R5. During any cycle, the execution lane 601 may read from orwrite to any of registers R1 through R5. For instructions requiring twoinput operands the execution lane may retrieve both of operands from anyof R1 through R5.

In an embodiment, the two dimensional shift register structure isimplemented by permitting, during a single cycle, the contents of any of(only) one of registers R2 through R4 to be shifted “out” to one of itsneighbor's register files through output multiplexer 603, and, havingthe contents of any of (only) one of registers R2 through R4 replacedwith content that is shifted “in” from a corresponding one if itsneighbors through input multiplexers 604 such that shifts betweenneighbors are in a same direction (e.g., all execution lanes shift left,all execution lanes shift right, etc.). Although it may be common for asame register to have its contents shifted out and replaced with contentthat is shifted in on a same cycle, the multiplexer arrangement 603, 604permits for different shift source and shift target registers within asame register file during a same cycle.

As depicted in FIG. 6a note that during a shift sequence an executionlane will shift content out from its register file 602 to each of itsleft, right, top and bottom neighbors. In conjunction with the sameshift sequence, the execution lane will also shift content into itsregister file from a particular one of its left, right, top and bottomneighbors. Again, the shift out target and shift in source should beconsistent with a same shift direction for all execution lanes (e.g., ifthe shift out is to the right neighbor, the shift in should be from theleft neighbor).

Although in one embodiment the content of only one register is permittedto be shifted per execution lane per cycle, other embodiments may permitthe content of more than one register to be shifted in/out. For example,the content of two registers may be shifted out/in during a same cycleif a second instance of the multiplexer circuitry 603, 604 observed inFIG. 6a is incorporated into the design of FIG. 6 a. Of course, inembodiments where the content of only one register is permitted to beshifted per cycle, shifts from multiple registers may take place betweenmathematical operations by consuming more clock cycles for shiftsbetween mathematical operations (e.g., the contents of two registers maybe shifted between math ops by consuming two shift ops between the mathops).

If less than all the content of an execution lane's register files areshifted out during a shift sequence note that the content of the nonshifted out registers of each execution lane remain in place (do notshift). As such, any non shifted content that is not replaced withshifted in content persists local to the execution lane across theshifting cycle. The memory unit (“M”) observed in each execution lane isused to load/store data from/to the random access memory space that isassociated with the execution lane's row and/or column within theexecution lane array. Here, the M unit acts as a standard M unit in thatit is often used to load/store data that cannot be loaded/stored from/tothe execution lane's own register space. In various embodiments, theprimary operation of the M unit is to write data from a local registerinto memory, and, read data from memory and write it into a localregister.

With respect to the ISA opcodes supported by the ALU unit of thehardware execution lane 601, in various embodiments, the mathematicalopcodes supported by the hardware ALU are integrally tied with (e.g.,substantially the same as) the mathematical opcodes supported by avirtual execution lane (e.g., ADD, SUB, MOV, MUL, MAD, ABS, DIV, SHL,SHR, MIN/MAX, SEL, AND, OR, XOR, NOT). As described just above, memoryaccess instructions can be executed by the execution lane 601 tofetch/store data from/to their associated random access memory.Additionally the hardware execution lane 601 supports shift opinstructions (right, left, up, down) to shift data within the twodimensional shift register structure. As described above, programcontrol instructions are largely executed by the scalar processor of thestencil processor.

FIG. 7a depicts an embodiment of a “top down” view of the logical (andpotentially physical) design of a two-dimensional register arraystructure. The “top-down” view of FIG. 7a essentially conforms to theunit cell design embodiment of FIG. 6 in which each register file at aparticular array location is coupled to the register file of its left,right, up and down neighboring unit cell location. That is, for example,as seen in FIG. 7 a, register file A is coupled to register files B, C,D and E.

FIG. 7b depicts another embodiment of a “top-down” view of the logical(and potentially physical) design of a two-dimensional register arraystructure. As observed in FIG. 7 b, unit cells are not only coupled tonearest vertical and horizontal neighbors, but also “second” nearestvertical and horizontal neighbors. For example, as observed in FIG. 7 b,unit cell A is not only coupled to unit cells B, C, D and E but is alsocoupled to unit cells F, G, H and I. For ease of drawing and viewing,only unit cell A is depicted as having the full set of connectionsneeded to have both nearest and second nearest neighbor coupling. Otherthan unit cell A, only every other unit cell shows second nearestneighbor coupling along any particular row or column (e.g., unit cell Bdoes not depict any second nearest neighbor coupling). The reader willunderstand that a preferred embodiment would include the coupling ofunit cell A for, e.g., all the unit cells within the core andsufficiently away from array edges to support second nearest neighborcoupling.

Having second nearest connection provides for faster propagation of theregister values through the register array. For example, if a registervalue needs to be moved to a unit cell four locations away, the arraystructure of FIG. 7b can accomplish the move in two cycles whereas thearray structure of FIG. 7b can accomplish the same move in only fourcycles. Note that the embodiment of FIG. 7b also has nearest neighborconnections. Thus, the execution lane instruction set for the structureof FIG. 7b may be more expansive than the execution lane instruction setfor the structure of FIG. 7a (the former having one-hop and two-hop MOVinstructions whereas the latter only has one-hop MOV instructions).

It is pertinent to point out that the number and combination ofdifferent numbered hop movements and corresponding array structureembodiments may widely vary from embodiment to embodiment depending onthe appropriate trade off balance between the need for rapid registervalue movement and the tolerance for array structure wiring density.Some embodiments may support nearest third or and/or fourth neighborconnections, others may not (in the case of nearest fourth neighborconnections, e.g., unit cell D would be directly coupled to unit cell Jin FIG. 7b ). Some embodiments may have only nearest neighborconnections and nearest third or farther connections, etc. Conceivably,more elaborate embodiments may even support diagonal connections (e.g.,connecting unit cell A with unit cell K and its other three neighboringcorner unit cells in FIG. 7b ). Those of ordinary skill will recognizethat any of the various, expanded connections amongst unit cells isreadily accomplished by expanding the sources of the inputs to the inputmux structure 604 and expanding the fan-out from the output muxstructure 603 of FIG. 6.

FIG. 8a shows an exemplary logical arrangement of registers along a rowor column within a two dimensional register array structure (for ease ofdrawing the register array only has dimensions of 8×8, whereas, inactual practice the dimensions may be much larger). Here, neighboringpixels in an array being processed will be located in numericallyneighboring units cells (e.g., a pair of neighboring pixels in the arraywill be placed in unit cells 3 and 4 rather than 3 and 5). The logicaldesign of FIG. 8a also includes a roll capability by coupling the firstlogical unit cell 1 to the last unit cell 8 through connection 801 (thusthe execution lanes of the execution lane array may also include a rollopcode).

Problems may arise however, particularly in the case of arrays of largedimension, if the design of FIG. 8a not only represents the logicaldesign but also represents the physical design. If the approach of FIG.8a also represents the physical design, connection 801 corresponds to anextremely long length wire as compared to the length of the other wiresthat connect unit cell pairs other than pair 1 and 8. This particularwire length outlier can cause circuit timing complications (by slowingdown all shift times between all unit cells to be no less than theslowest 1<−>8 shift time, or, introducing complications that recognizemore cycles between 1<−>8 shifts than shifts between any otherneighboring unit cells).

FIG. 8b shows an embodiment of an improved physical design for a row orcolumn of a register array structure having the logical design of FIG. 8a. Here, a physical design corresponds to actual layout of circuitstructures as opposed to just logical connections (as with a logicaldesign). As observed in FIG. 8 b, the physical design amortizes theextra length required by the 1<−>8 connection amongst the other unitcell by imposing a toroid design in the logic of the layout. Forexample, although unit cell 1 is physically connected to unit cell 2 topreserve the logic design, unit cell 8 physically sits between them. Theresultant is a maximum wire length between unit cells in the structureof FIG. 8b that is much shorter than the length of wire 801 in FIG. 8 a,As such the timing complications of the structure of FIG. 8b avoid thetiming complications of the structure of FIG. 8a mentioned above. In anembodiment, a roll of register content between all unit cells cantranspire within a single cycle.

FIG. 8c shows that the data bus structure between the sheet generator ora random access memory 802 (such as any of RAMs 407 of FIG. 4) and a rowor column of the register array include a kind of swizzling structure803 in order to preserve the correct logic connections to an array orrow having a toroid physical layout. FIG. 8d shows another toroidstructure that can implement 4-hop shifts where the maximum distancetraveled by any register value is 4 unit cells. Here, it should be clearthat another swizzling like data bus would exist between the registersof FIG. 8d and the sheet generator or RAM. As such, a feature of theimplementation of a toroid physical layout is the existence of swizzlingby a data bus that connects inputs that are arranged in logical order.

FIG. 8e shows special fan-out circuitry from the output multiplexer 804of a unit cell of the shift array structure. Here, output multiplexer804 can be viewed as akin to output multiplexer 603 of FIG. 6 a. As theshift array is designed to support more and more connections (one hop,two hop, etc.), the fan-out of the output multiplexer 804 grows. As thefan-out of the multiplexer 804 grows, power consumption may become moreand more of an issue. FIG. 8e shows an output multiplexer 804 for ashift register array that fully supports both one hop and twoconnections. Here, without the presence of the logic gates observed inFIG. 8 e, a new output at multiplexer 804 (e.g., a new shift out value)would be broadcast to eight different locations (left neighbor, rightneighbor, . . . , 2 hop bottom neighbor). Here, as is understood in theart, a change in data across a run length of wire in a logical circuitcorresponds to “switching activity” which, in turn, consumes power.

The presence of the eight logic gates observed at the output ofmultiplexer 804 are designed to prevent any such data change except onthe actual wire that corresponds to the shift direction. For example, ifthe shift direction is one-hop to the right, only the gate that iscoupled to the immediate right neighbor will permit the output of themultiplexer 804 to pass. All other logic gates will prevent the datavalue from propagating to the other nodes (where the shift value is notneeded) and reduce power consumption of the shift operation in theprocess.

c. Implementation Embodiments

It is pertinent to point out that the various image processorarchitecture features described above are not necessarily limited toimage processing in the traditional sense and therefore may be appliedto other applications that may (or may not) cause the image processor tobe re-characterized. For example, if any of the various image processorarchitecture features described above were to be used in the creationand/or generation and/or rendering of animation as opposed to theprocessing of actual camera images, the image processor may becharacterized as a graphics processing unit. Additionally, the imageprocessor architectural features described above may be applied to othertechnical applications such as video processing, vision processing,image recognition and/or machine learning. Applied in this manner, theimage processor may be integrated with (e.g., as a co-processor to) amore general purpose processor (e.g., that is or is part of a CPU ofcomputing system), or, may be a stand alone processor within a computingsystem.

The hardware design embodiments discussed above may be embodied within asemiconductor chip and/or as a description of a circuit design foreventual targeting toward a semiconductor manufacturing process. In thecase of the later, such circuit descriptions may take of the form ofhigher/behavioral level circuit descriptions (e.g., a VHDL description)or lower level circuit description (e.g., a register transfer level(RTL) description, transistor level description or mask description) orvarious combinations thereof. Circuit descriptions are typicallyembodied on a computer readable storage medium (such as a CD-ROM orother type of storage technology).

From the preceding sections is pertinent to recognize that an imageprocessor as described above may be embodied in hardware on a computersystem (e.g., as part of a handheld device's System on Chip (SOC) thatprocesses data from the handheld device's camera). In cases where theimage processor is embodied as a hardware circuit, note that the imagedata that is processed by the image processor may be received directlyfrom a camera. Here, the image processor may be part of a discretecamera, or, part of a computing system having an integrated camera. Inthe case of the later the image data may be received directly from thecamera or from the computing system's system memory (e.g., the camerasends its image data to system memory rather than the image processor).Note also that many of the features described in the preceding sectionsmay be applicable to a graphics processor unit (which rendersanimation).

FIG. 9 provides an exemplary depiction of a computing system. Many ofthe components of the computing system described below are applicable toa computing system having an integrated camera and associated imageprocessor (e.g., a handheld device such as a smartphone or tabletcomputer). Those of ordinary skill will be able to easily delineatebetween the two.

As observed in FIG. 9, the basic computing system may include a centralprocessing unit 901 (which may include, e.g., a plurality of generalpurpose processing cores 915_1 through 915_N and a main memorycontroller 917 disposed on a multi-core processor or applicationsprocessor), system memory 902, a display 903 (e.g., touchscreen,flat-panel), a local wired point-to-point link (e.g., USB) interface904, various network I/O functions 905 (such as an Ethernet interfaceand/or cellular modem subsystem), a wireless local area network (e.g.,WiFi) interface 906, a wireless point-to-point link (e.g., Bluetooth)interface 907 and a Global Positioning System interface 908, varioussensors 909_1 through 909_N, one or more cameras 910, a battery 911, apower management control unit 912, a speaker and microphone 913 and anaudio coder/decoder 914.

An applications processor or multi-core processor 950 may include one ormore general purpose processing cores 915 within its CPU 901, one ormore graphical processing units 916, a memory management function 917(e.g., a memory controller), an I/O control function 918 and an imageprocessing unit 919. The general purpose processing cores 915 typicallyexecute the operating system and application software of the computingsystem. The graphics processing units 916 typically execute graphicsintensive functions to, e.g., generate graphics information that ispresented on the display 903. The memory control function 917 interfaceswith the system memory 902 to write/read data to/from system memory 902.The power management control unit 912 generally controls the powerconsumption of the system 900.

The image processing unit 919 may be implemented according to any of theimage processing unit embodiments described at length above in thepreceding sections. Alternatively or in combination, the IPU 919 may becoupled to either or both of the GPU 916 and CPU 901 as a co-processorthereof. Additionally, in various embodiments, the GPU 916 may beimplemented with any of the image processor features described at lengthabove.

Each of the touchscreen display 903, the communication interfaces 904907, the GPS interface 908, the sensors 909, the camera 910, and thespeaker/microphone codec 913, 914 all can be viewed as various forms ofI/O (input and/or output) relative to the overall computing systemincluding, where appropriate, an integrated peripheral device as well(e.g., the one or more cameras 910). Depending on implementation,various ones of these I/O components may be integrated on theapplications processor/multi-core processor 950 or may be located offthe die or outside the package of the applications processor/multi-coreprocessor 950.

In an embodiment one or more cameras 910 includes a depth camera capableof measuring depth between the camera and an object in its field ofview. Application software, operating system software, device driversoftware and/or firmware executing on a general purpose CPU core (orother functional block having an instruction execution pipeline toexecute program code) of an applications processor or other processormay perform any of the functions described above.

Embodiments of the invention may include various processes as set forthabove. The processes may be embodied in machine-executable instructions.The instructions can be used to cause a general-purpose orspecial-purpose processor to perform certain processes. Alternatively,these processes may be performed by specific hardware components thatcontain hardwired logic for performing the processes, or by anycombination of programmed computer components and custom hardwarecomponents.

Elements of the present invention may also be provided as amachine-readable medium for storing the machine-executable instructions.The machine-readable medium may include, but is not limited to, floppydiskettes, optical disks, CD-ROMs, and magneto-optical disks, FLASHmemory, ROMs, RAMs, EPROMs, EEPROMs, magnetic or optical cards,propagation media or other type of media/machine-readable mediumsuitable for storing electronic instructions. For example, the presentinvention may be downloaded as a computer program which may betransferred from a remote computer (e.g., a server) to a requestingcomputer (e.g., a client) by way of data signals embodied in a carrierwave or other propagation medium via a communication link (e.g., a modemor network connection).

In the foregoing specification, the invention has been described withreference to specific exemplary embodiments thereof. It will, however,be evident that various modifications and changes may be made theretowithout departing from the broader spirit and scope of the invention asset forth in the appended claims. The specification and drawings are,accordingly, to be regarded in an illustrative rather than a restrictivesense.

1. A processor comprising: a plurality of execution lanes, eachexecution lane comprising logic circuitry capable of executinginstructions; and a two-dimensional shift-register array comprising aplurality of electrically coupled shift registers, wherein eachexecution lane is configured to shift data from a respective shiftregister dedicated to the execution lane to one or more adjacent shiftregisters in the two-dimensional shift-register array, each of the oneor more adjacent shift registers being a shift register dedicated to adifferent execution lane.
 2. The processor of claim 1, wherein eachexecution lane of the plurality of execution lanes comprises anarithmetic logic unit configured to read from and write to one or moreshift registers dedicated to the execution lane.
 3. The processor ofclaim 1, wherein all execution lanes of the plurality of execution lanesare configured to shift data in the shift registers in the samespecified direction.
 4. The processor of claim 1, wherein the processoris configured to receive a shift instruction that specifies a directionalong one of the two dimensions of the two-dimensional shift-registerarray, and to broadcast data representing the specified direction toeach of the plurality of execution lanes.
 5. The processor of claim 4,wherein the execution lanes are configured to shift data in thetwo-dimensional shift-register array along a same direction of thetwo-dimensional shift-register array in response to receiving thedirection as part of the shift instruction.
 6. The processor of claim 1,wherein the processor is configured to receive a sheet oftwo-dimensional image data and to store discrete portions of the sheetof two-dimensional image data in corresponding shift registers of thetwo-dimensional shift-register array.
 7. The processor of claim 1,wherein each execution lane is configured to shift data from a shiftregister dedicated to the execution lane to a neighboring shift registerwithout reading to or writing from random access memory.
 8. Theprocessor of claim 1, wherein each execution lane is configured to shiftdata from a shift register dedicated to the execution to a neighboringshift register without the data being processed by an arithmetic logicunit of the execution lane.
 9. The processor of claim 1, wherein eachexecution lane has two or more different types of dedicated registers,including one or more dedicated shift registers and one or morededicated temporary registers, wherein an arithmetic logic unit of eachexecution lane is configured to read to and write from the one or morededicated shift registers and one or more dedicated temporary registersof the execution lane.
 10. The processor of claim 1, further comprising:a plurality of halo execution lanes, wherein each halo execution lanehas one or more shift registers of the plurality of shift registers inthe two-dimensional shift-register array, wherein the shift registersthat are dedicated to the halo execution lanes are shift registers thatare located along edges of the two-dimensional shift-register array. 11.The processor of claim 10, wherein each halo execution lane of theplurality of halo execution lanes lacks an arithmetic logic unit.
 12. Acomputer-implemented method comprising: receiving, by each executionlane of a plurality of execution lanes in a processor, an instruction toshift data in a two-dimensional shift-register array comprising aplurality of electrically coupled shift registers, wherein eachexecution lane comprises logic circuitry capable of executioninstructions, wherein each execution lane is configured to shift datafrom a respective shift register dedicated to the execution lane to oneor more adjacent shift registers in the two-dimensional shift-registerarray, each of the one or more adjacent shift registers being a shiftregister dedicated to a different execution lane; and shifting, by eachexecution lane of the plurality of execution lanes, data in a respectiveshift register dedicated to the execution lane to one or more adjacentshift registers in the two-dimensional shift-register array in responseto receiving the instruction.
 13. The method of claim 12, wherein eachexecution lane of the plurality of execution lanes comprises anarithmetic logic unit configured to read from and write to one or moreshift registers dedicated to the execution lane.
 14. The method of claim12, wherein shifting, by each execution lane, data in a respective shiftregister dedicated to the execution lane comprises shifting, by allexecution lanes of the plurality of execution lanes, the data in thetwo-dimensional shift-register array in the same specified direction.15. The method of claim 12, wherein the instruction specifies adirection along one of the two dimensions of the two-dimensionalshift-register array, and further comprising broadcasting, by theprocessor, data representing the specified direction to each of theplurality of execution lanes.
 16. The method of claim 15, wherein theexecution lanes are configured to shift data in the two-dimensionalshift-register array along a same direction of the two-dimensionalshift-register array in response to receiving the direction as part ofthe instruction.
 17. The method of claim 12, further comprising:receiving, by the processor, a sheet of two-dimensional image data; andstoring, by the processor, discrete portions of the sheet oftwo-dimensional image data in corresponding shift registers of thetwo-dimensional shift-register array.
 18. The method of claim 12,wherein shifting, by each execution lane, the data comprises shiftingthe data from a shift register dedicated to the execution lane to aneighboring shift register without reading to or writing from randomaccess memory.
 19. The method of claim 12, wherein shifting, by eachexecution lane, the data comprises shifting the data from a shiftregister dedicated to the execution to a neighboring shift registerwithout processing the data by an arithmetic logic unit of the executionlane.
 20. The method of claim 12, wherein each execution lane has two ormore different types of dedicated registers, including one or morededicated shift registers and one or more dedicated temporary registers,wherein an arithmetic logic unit of each execution lane is configured toread to and write from the one or more dedicated shift registers and oneor more dedicated temporary registers of the execution lane.
 21. Themethod of claim 12, wherein shifting, by each execution lane, the datacomprises shifting, by one or more execution lanes, data into a one ormore shift registers dedicated to one or more halo execution lanes,wherein the shift registers that are dedicated to the halo executionlanes are shift registers that are located along edges of thetwo-dimensional shift-register array.
 22. The method of claim 21,wherein each halo execution lane of the one or more halo execution laneslacks an arithmetic logic unit.